DRM bridges are not visible to the userspace and it may not be immediately clear if the chain is somehow constructed incorrectly. I have had two separate instances of a bridge driver failing to do a drm_bridge_attach() call, resulting in the bridge connector not being part of the chain. In some situations this doesn't seem to cause issues, but it will if DRM_BRIDGE_ATTACH_NO_CONNECTOR flag is used. Add a debugfs file to print the bridge chains. For me, on this TI AM62 based platform, I get the following output: encoder[39] bridge[0] type: 0, ops: 0x0 bridge[1] type: 0, ops: 0x0, OF: /bus@f0000/i2c@20000000/dsi@e:toshiba,tc358778 bridge[2] type: 0, ops: 0x3, OF: /bus@f0000/i2c@20010000/hdmi@48:lontium,lt8912b bridge[3] type: 11, ops: 0x7, OF: /hdmi-connector:hdmi-connector Signed-off-by: Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx> --- Changes in v2: - Fixed compilation issue when !CONFIG_OF - Link to v1: https://lore.kernel.org/r/20230721-drm-bridge-chain-debugfs-v1-1-8614ff7e890d@xxxxxxxxxxxxxxxx --- drivers/gpu/drm/drm_bridge.c | 50 +++++++++++++++++++++++++++++++++++++++++++ drivers/gpu/drm/drm_debugfs.c | 3 +++ include/drm/drm_bridge.h | 5 +++++ 3 files changed, 58 insertions(+) diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c index c3d69af02e79..d3eb62d5ef3b 100644 --- a/drivers/gpu/drm/drm_bridge.c +++ b/drivers/gpu/drm/drm_bridge.c @@ -27,8 +27,10 @@ #include <linux/mutex.h> #include <drm/drm_atomic_state_helper.h> +#include <drm/drm_debugfs.h> #include <drm/drm_bridge.h> #include <drm/drm_encoder.h> +#include <drm/drm_file.h> #include <drm/drm_of.h> #include <drm/drm_print.h> @@ -1345,6 +1347,54 @@ struct drm_bridge *of_drm_find_bridge(struct device_node *np) EXPORT_SYMBOL(of_drm_find_bridge); #endif +#ifdef CONFIG_DEBUG_FS +static int drm_bridge_chains_info(struct seq_file *m, void *data) +{ + struct drm_debugfs_entry *entry = m->private; + struct drm_device *dev = entry->dev; + struct drm_printer p = drm_seq_file_printer(m); + struct drm_mode_config *config = &dev->mode_config; + struct drm_encoder *encoder; + unsigned int bridge_idx = 0; + + list_for_each_entry(encoder, &config->encoder_list, head) { + struct drm_bridge *bridge; + + drm_printf(&p, "encoder[%u]\n", encoder->base.id); + + bridge = drm_bridge_chain_get_first_bridge(encoder); + + while (bridge) { + drm_printf(&p, "\tbridge[%u] type: %u, ops: %#x", + bridge_idx, bridge->type, bridge->ops); + +#ifdef CONFIG_OF + if (bridge->of_node) + drm_printf(&p, ", OF: %pOFfc", bridge->of_node); +#endif + + drm_printf(&p, "\n"); + + bridge_idx++; + bridge = drm_bridge_get_next_bridge(bridge); + } + } + + return 0; +} + +/* any use in debugfs files to dump individual planes/crtc/etc? */ +static const struct drm_debugfs_info drm_bridge_debugfs_list[] = { + {"bridge_chains", drm_bridge_chains_info, 0}, +}; + +void drm_bridge_debugfs_init(struct drm_minor *minor) +{ + drm_debugfs_add_files(minor->dev, drm_bridge_debugfs_list, + ARRAY_SIZE(drm_bridge_debugfs_list)); +} +#endif + MODULE_AUTHOR("Ajay Kumar <ajaykumar.rs@xxxxxxxxxxx>"); MODULE_DESCRIPTION("DRM bridge infrastructure"); MODULE_LICENSE("GPL and additional rights"); diff --git a/drivers/gpu/drm/drm_debugfs.c b/drivers/gpu/drm/drm_debugfs.c index c90dbcffa0dc..3e89559d68cd 100644 --- a/drivers/gpu/drm/drm_debugfs.c +++ b/drivers/gpu/drm/drm_debugfs.c @@ -31,6 +31,7 @@ #include <drm/drm_atomic.h> #include <drm/drm_auth.h> +#include <drm/drm_bridge.h> #include <drm/drm_client.h> #include <drm/drm_debugfs.h> #include <drm/drm_device.h> @@ -272,6 +273,8 @@ int drm_debugfs_init(struct drm_minor *minor, int minor_id, drm_debugfs_add_files(minor->dev, drm_debugfs_list, DRM_DEBUGFS_ENTRIES); + drm_bridge_debugfs_init(minor); + if (drm_drv_uses_atomic_modeset(dev)) { drm_atomic_debugfs_init(minor); } diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h index bf964cdfb330..60dbee6bd1e6 100644 --- a/include/drm/drm_bridge.h +++ b/include/drm/drm_bridge.h @@ -949,4 +949,9 @@ static inline struct drm_bridge *drmm_of_get_bridge(struct drm_device *drm, } #endif +#ifdef CONFIG_DEBUG_FS +struct drm_minor; +void drm_bridge_debugfs_init(struct drm_minor *minor); +#endif + #endif --- base-commit: c7a472297169156252a50d76965eb36b081186e2 change-id: 20230721-drm-bridge-chain-debugfs-0bbc1522f57a Best regards, -- Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx>
